Novel sulfonated Nafion®-based composite membranes with pillararene as selective artificial proton channels for application in direct methanol fuel cells

• Novel proton exchange membranes were synthesized for use in direct methanol fuel cells.
• The composite membranes included pillar[5]arene as artificial proton channels.
• The membranes had greater proton conductivity and methanol resistance than Nafion.

Proton exchange membranes (PEM) are critical components of low temperature fuel cells. Most PEMs are made of perfluorinated sulfonic acid polymers such as Nafion®. However, Nafion has a high methanol permeability which is limiting its applicability in direct methanol fuel cells (DMFCs). Here, we report on novel sulfonated pillar[5]arene/Nafion composite membranes with improved properties for application in DMFCs. The properties of the novel composite membranes were investigated under a range of synthesis and operating conditions. Under most conditions, the novel composite membranes exhibited properties far superior than Nafion. For example, the proton conductivity of the sulfonated pillar[5]arene's (10 wt.%)/Nafion composite membrane was 0.145 × 10−4 S cm−1 at 80 °C, while methanol permeability was 2.43 × 10−6 cm2/s. Proton selectivity was increased up to two-fold compared to Nafion-recast membrane. The likely mechanisms for improvements were discussed. Overall, these results indicate that these novel composite membranes are promising for application in DMFCs.